Method and Apparatus for Identifying Pulses in Detector Output Data

1. A method for locating a pulse in detector output data, comprising: generating, by a detector circuit, detector output data comprising at least one pulse corresponding to a radiation event in radiation received at the detector circuit from a specimen; receiving, at a processor circuit, the detector output data from the detector circuit; sliding, by the processor circuit, a window across the detector output data to successive window locations; identifying possible pulses by fitting one or more functions to the detector output data in the window at each of the window locations; determining which of the possible pulses have: i) a pulse start falling one, two or three samples before the start of the respective window location and ii) a peak amplitude exceeding the standard deviation of noise in the window at the respective window location; identifying as pulses those of said possible pulses that have: i) a pulse start falling one, two or three samples before the start of the respective window location and ii) a peak amplitude exceeding the standard deviation of the noise in the window at the respective window location; determining a location and the peak amplitude of each of the identified pulses from the one or more functions determined by said fitting; and employing security measures, diagnosing a medical condition, logging an oil well, screening goods, or locating an object based on the determined location and/or the determined peak amplitude of each of the identified pulses.

2. A method as claimed in claim 1 , wherein said one or more functions are a function of time.

3. A method as claimed in claim 1 , comprising providing said data in, or converting said data into, digital form before fitting said one or more functions to said data.

4. A method as claimed in claim 1 , comprising: generating said detector output data by applying a mathematical transform to said detector output data, said mathematical transform being selected according to an expected form of said pulse.

5. A method as claimed in claim 1 , wherein said fitting includes: fitting a plurality of functions to the detector output data; and determining a function of best fit, being whichever of said plurality of functions optimizes a chosen metric when modelling said data; and said determining includes determining the location and amplitude of said peak from the determined function of best fit.

6. A method as claimed in claim 1 , comprising: determining error residuals from said fitting; and determining a baseline offset of said detector output from said error residuals.

8. A method as claimed in claim 1 , including determining a location and amplitude of the pulse with a method comprising: defining a reference pulse p(t) as a convolution of e −αt u(t) with e −βt u(t), and determining the location τ and amplitude A of ƒ(t) from ƒ(t)=Ap(t−τ), with τ≤0.

10. A method as claimed in claim 1 , comprising forcing any estimates having the pulse starting within a window to start at a boundary of said window.

11. A method as claimed in claim 1 , comprising maximizing window size or varying window size.

12. A method as claimed in claim 1 , wherein said determining the location of the peak comprises minimizing an offset between the start of a window and a start of the pulse.

13. A method as claimed in claim 1 , wherein each of said one or more functions is a superposition of a plurality of functions, the method comprising low-pass filtering the detector output data before fitting said one or more functions; and the method comprising adapting said one or more functions to allow for a low frequency artifact in said detector output data.

14. A method as claimed in claim 1 , comprising transforming said detector output data with a transform before fitting said one or more functions to the detector output data as transformed, wherein said transform is a Laplace transform or a Fourier transform.

15. A method as claimed in claim 14 , wherein each of said one or more functions is a superposition of a plurality of functions.

16. A method as claimed in claim 1 : wherein identifying possible pulses further comprises performing pulse fitting of either said function of best fit or of said plurality of functions to the data in the window at each window location.

17. A method for determining baseline offset, comprising: fitting one or more functions to detector output data according to the method of claim 1 ; determining error residuals from fitting said one or more functions; and determining said baseline offset from said error residuals.